[Trac #1412] Switch from driving the panel from the Geode to the DCON when the display is idle.

[Zarro Boogs per Child]

#1412: Switch from driving the panel from the Geode to the DCON when the display
is idle.
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 Reporter:  jg               |        Owner:  rsmith
     Type:  enhancement      |       Status:  new   
 Priority:  normal           |    Milestone:  CTest 
Component:  x window system  |   Resolution:        
 Keywords:                   |  
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Comment (by JordanCrouse):

 Bear in mind - it will cost us up to a frame of time to switch back into
 CPU mode.  The DCON always keeps a frames worth of data in its internal
 memory; so when we switch back to CPU mode, we have to wait for a frames
 worth of data to fill the memory before switching back to CPU mode,
 otherwise, the DCON will gitch, @56Hz, thats at most a 17ms delay.

 At one time, we also suffered the 64ms delay of turning back on the panel
 power (which has no effect on our actual power usage, but the bit also
 controls the panel data pins, so it must be enabled).  I think we can
 safely leave the panel power on when we switch into DCON mode.  I believe
 it will cost us a little more power, but with the shorter delay, we can
 switch into DCON mode more often.

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Ticket URL: <http://dev.laptop.org/ticket/1412#comment:2>
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